Molluscum contagiosum virions were isolated from clinically typical skin lesions and the DNA extracted and characterized using techniques of electron microscopy and agarose gel electrophoresis. The structure characteristics determined in these studies tend to place the MCV genome among other members of the poxvirus group in terms of genome molecular weight and organization. The apparent denaturability of the MCV genome into a continuous, single-stranded circle would point to the presence of terminal cross-links in the DNA molecule. So far, this structural arrangement appears to be unique to members of the poxvirus group. The objective of these studies has been to define structural features of these molecules and to relate them to the biochemical events involved in the replication and growth of this virus in the cells they infect.